Influence of the Fe Concentration on the Superconducting Properties of Fe1-ySe

Abstract

We present a comparative study of electrical transport properties in the normal state and in the dissipative superconducting state between pure β-FeSe phase and Fe deficient Fe1−y Se crystals. We discuss the influence of the intergrowth of the magnetic hexagonal phase (Fe7 Se8 ) in Fe deficient samples when compared to pure β-FeSe samples. In the superconducting state, we measured the ab-plane electrical resistivity with magnetic field up to 16 T and the electrical resistivity as a function of the angle between the c axis and the applied field. The angular dependence at fixed temperature below the superconducting critical temperature, Tc(H = 0), is very different for both sets of crystals. The Fe deficient samples display a vortex pinning-related feature at ∼57◦ off the plane while the pure β-FeSe phase samples show the persistence of a strong angular-dependent magnetoresistance characteristic of the normal state electronic structure.